1. Field of the Invention
This invention relates to a method for protecting healthy tooth surfaces against erosion by an acid etching agent utilized in tooth restoration treatments and to a varnish for forming a temporary coated layer on tooth surfaces during said treatment.
2. Description of the Prior Art
A method which has been widely used in the past for restoring teeth comprises removing the caries portion of the tooth and filling the cavity with a composite resin to restore the tooth. In this method, adhesion of the composite resin to the tooth is a problem, and if the adhesion is poor, the filling falls from the tooth or further caries development occurs between the tooth and the filling. For this reason, it is necessary to improve the adhesion between resin and cavity surfaces, and it is common practice to treat the tooth surface with an acid etching agent comprising an aqueous solution of phosphoric acid, citric acid or the like and further coating the surfaces of the cavity with a bonding agent containing an adhesive monomer before filling the cavity with the composite resin [J. Dent. Res., 34, 849 (1955), U.S. Pat. No. 4,259,075]. Although the acid etching agent is effective in promoting enhanced adhesion between the composite resin and the surfaces of the cavity by providing a minutely irregular tooth surface, the method has the disadvantage that, if the acid treating agent spreads over into healthy tooth surfaces, it also etches the healthy tooth surfaces (especially the enamel) thereby forming an irregular etched surface upon which dental plaque forms and to which the bacteria cling, thus leading to the formation of caries. In order to prevent this situation, the viscosity of the acid etchant has been increased in order to limit the flow and spread of the etchant to adjacent areas by adding carboxy-methyl cellulose or highly dispersed, submicron size silica to the acid aqueous solution (Japanese Patent application Laid-Open No. 36994/1978). However, such an etchant is difficult to apply to only the caries portion of the tooth, and therefore it is difficult, if not impossible, to avoid the spreading of the acid etchant to nearby healthy tooth surfaces. A need therefore continues to exist for an improved method of applying and acid etchants to restricted areas of tooth surfaces.